How Cordless Telephones Work

Diagram showing how the base unit and handset of the cordless phone talk to each other: Each color represents a different frequency.

A cordless telephone is basically a combination telephone and radio transmitter/receiver (see How Telephones Work and How Radio Works for details on these two technologies). A cordless phone has two major parts: base and handset.

The base is attached to the phone jack through a standard phone wire connection, and as far as the phone system is concerned it looks just like a normal phone. The base receives the incoming call (as an electrical signal) through the phone line, converts it to an FM radio signal and then broadcasts that signal.

The handset receives the radio signal from the base, converts it to an electrical signal and sends that signal to the speaker, where it is converted into the sound you hear. When you talk, the handset broadcasts your voice through a second FM radio signal back to the base. The base receives your voice signal, converts it to an electrical signal and sends that signal through the phone line to the other party.

The base and handset operate on a frequency pair that allows you to talk and listen at the same time, called duplex frequency.